Computational study on kinetics and mechanism of Cl-initiated hydrogen abstraction of methyl fluoroacetate Bhupesh Kumar Mishra a,b, * a Department of Chemical Sciences, Tezpur University, Tezpur 784 028, Assam, India b Department of Chemistry, D. N. Government College, Itanagar 791113, Arunachal Pradesh, India 1. Introduction Hydrofluoroethers (HFEs) have been the focus of intense attention as replacement materials for CFCs and hydrochloro- fluorocarbons (HCFCs) in industrial applications such as heat- transfer fluid in refrigeration systems, cleaning agent in electronic industry, foam-blowing and also for lubricant deposi- tion [1,2]. It has been reported that fluorinated esters (FESs) are the primary products of the atmospheric oxidation of HFEs [3]. For instance, the fluoroakylformates C 4 F 9 OC(O)H and n- C 3 F 7 OC(O)H are the major degradation products of HFE-7100 (C 4 F 9 OCH 3 ) and HFE-7000 (C 3 F 7 OCH 3 ), respectively [4,5]. Simi- larly, methyl trifluoroacetate CH 3 OC(O)CF 3 is the major degra- dation product of OH-initiated oxidation of CH 3 OCH(CF 3 ) 2 [6]. These fluorinated compounds find wide applications in biochemistry, medicinal chemistry, pharmacology and related fields [7,8]. The substitution of hydrogen by fluorine in pharmacologically active organic molecules can have profound effects on the activity [9]. Fluoroacetate (FA; CH 2 FCOOR) is highly toxic towards humans and other mammals through inhibition of the enzyme aconitase in the tricarboxylic acid cycle, caused by ‘lethal synthesis’ of an isomer of fluorocitrate (FC) [10]. The degradation of FESs produce environmentally burdened product like trifluoroacetic acid (TFA) which may impact on agricultural and aquatic systems [11]. Thus, it is important to study the kinetics and mechanistic degradation pathways of FESs for complete assessment of atmospheric chemistry as well as to explore the impact of FESs on the environment. Considerable attention has been paid in recent years to perform experimental and theoretical studies on the decomposition kinetics of FESs [12–24]. It is known that MFA was a substance of great toxicity, with very interesting pharmacological properties [25]. Like most volatile organic compounds (VOCs), reaction with OH radicals is considered to be the dominant removal process of esters in the troposphere [26]. Although global atmospheric abundance of OH radicals is around 2 orders of magnitude greater than that of chlorine atoms, Cl reactions are generally faster than OH reactions, so their contribution to the degradation of VOCs may be not negligible compared to the role of OH [27]. This contribution of Cl could be significant in areas where the concentration of Cl precursor species has been reported to be high, such as the coastal boundary layer [28]. In fact, chlorine atoms have been monitored in concentrations in the order of 10 5 molecule cm 3 over the marine boundary layer [29]. Thus, chlorine atom also plays an important role in atmospheric chemistry [30]. In earlier report [31] we theoretically investigated the product distribution of MFA by OH-initiated oxidation. The rate constant for the hydrogen abstraction by OH radicals Journal of Fluorine Chemistry 172 (2015) 74–79 A R T I C L E I N F O Article history: Received 20 November 2014 Received in revised form 26 January 2015 Accepted 30 January 2015 Available online 7 February 2015 Keywords: Fluoroesters Rate constant Atmospheric life time A B S T R A C T A theoretical investigation has been performed on the mechanism, kinetics and thermochemistry of the gas phase reactions of methyl fluoroacetate CH 2 FC(O)OCH 3 (MFA) with Cl atoms. Geometry optimization and frequency calculations have been made at the MPWB1K/6-31+G(d,p) level of theory and energetic information is further refined by calculating the energy of the species using G2(MP2) theory. The rate constant for reactions of MFA with Cl atoms are reported over wide range of 250–450 K using the Canonical Transition State Theory (CTST). The atmospheric lifetime of CH 2 FC(O)OCH 3 was estimated to be around 1.21 years with respect to reaction with Cl atoms. The rate constant obtained is compared with literature values for other similar species to establish reactivity trends. It is shown that the F-atom substitution decrease the reactivity of C–H bond of esters. ß 2015 Elsevier B.V. All rights reserved. * at: Chemical Sciences, Tezpur University, Tezpur 784028, Assam, India. Tel.: +91 3712267008; fax: +91 3712267005. E-mail addresses: bhupesh@tezu.ernet.in, bhupesh_chem@rediffmail.com Contents lists available at ScienceDirect Journal of Fluorine Chemistry jo ur n al h o mep ag e: www .elsevier .c om /loc ate/f luo r http://dx.doi.org/10.1016/j.jfluchem.2015.01.014 0022-1139/ß 2015 Elsevier B.V. All rights reserved.